(1) Field of the Invention
This invention relates to a transfer sheet. More particularly, the invention relates to a transfer sheet or a decalcomania for use in transferring pictures and designs to the surfaces of articles which are made of polyamide.
Polyamide resin is a polymer having amide bonds in its main chain and prepared by the polycondensation of diamines and dibasic acids, the ring opening-polymerization of lactams or the polycondensation of aminocarboxylic acids. The articles to receive transferred designs thereon are made by forming the above resin through blow molding, extrusion and injection molding. The transferring means that some designs are printed on base materials such as paper and then only the printed ink layers of designs are transferred on to the surfaces of articles by closely fitting the transfer sheets to the articles and heating under pressure.
(2) Description of the Prior Art
When designs are applied to the surfaces of polyamide articles in the conventional art, the direct methods such as silk screen printing, dry offset printing and so forth are employed. In these direct printing methods, however, the printing presses used for the methods are expensive, high printing techniques are required and large floor areas for equipments are necessary. Therefore, such methods are suitable for mass production. Further, in some cases, printed labels are applied to the surfaces of molded articles. However, it is defective in that the stuck labels are not durable against water and rubbing, and are liable to be peeled off.
In order to solve such the problems, the aforementioned design transferring method has been employed. In the transferring method, the transfer sheet has generally a thermosensitive adhesive layer which becomes adherent to the surface of article when heated.
However, there has been no adhesive which is adherent to polyamide resin. The ink used in the common direct printing method is tightly bonded to the surfaces of molded articles since reactive resins and curing agents are employed and reaction is caused to occur after the printing. When a non-reactive resin is used, sufficient strength or duability of the printed design cannot be expected. In the case of the transfer sheet, the reactive resin cannot be preserved in the form of rolled sheet to be used, therefore, the transfer sheet which gives sufficiently stron transferred designs has never been obtained.